Numerous types of sorting devices have been used in the past to sort objects by size. Prior sorting devices generally operate by dropping out objects of a particular size from a flow path of moving objects. Selection of the objects to be taken out of the flow path is accomplished by various techniques, for example, by sensors which measure the objects and control the opening and shutting of gates or doors to drop the objects out of the path, or by passing the objects over holes of various sizes with the holes dimensioned to drop objects of specific sizes out of the flow path.
U.S. Pat. No. 3,080,052 illustrates an example of a sorting apparatus which utilizes sensors. The sensors are placed in a path of transversely moving lumber. The sensors measure either width, length, thickness or grade of the lumber. When the sensor measures a piece of lumber with a particular width, length, thickness or grade which is to be selected, the sensor opens a gate through which the particular piece of lumber passes.
U.S. Pat. Nos. 2,662,640; 3,106,291; 3,150,022 and 3,469,690 disclose sorting apparatus wherein objects are selected by dropping through sized holes in a flow path. The '690 patent discloses a method and apparatus for sorting objects according to length, in particular wooden billets cut from rough log sections. The apparatus conveys the billets over a series of spaced conveyor belts. The spacing between the conveyor belts gradually increases between successive pairs of belts. Holding rollers are suspended at spaced positions above the inlet and discharge ends of each conveyor. The holding rollers at the discharge end of the conveyors apparently provide a certain amount of support for the billets passing over the discharge end of the conveyor, however, these rollers permit the billets to fall downwardly away from horizontal. If the billet is to be passed onto a successive conveyor belt, the billet comes into contact with an upwardly slanted run of the successive conveyor belt. The upwardly slanted run of the conveyor belt lifts the billet to a horizontal position where it then comes into contact with a holding roller located a distance above the horizontal run of the of the successive conveyor belt. Such a non-level flow of objects through a sorting system is undesirable, particularly when relatively high speed sorting is required. If the conveyors were run at relatively high speeds, the downwardly falling objects would strike the upwardly slanted run of a successive conveyor with higher force, possibly causing damage or contributing to belt failure.
A process has recently been developed for manufacturing structural wood products from long, relatively thin strands of wood by coating the strands with an adhesive, arranging the strands side-by-side in a lengthwise dimension of the lumber product and subjecting the arranged strands to compression. By this technique, a high strength dimensioned wood product can be formed. An example of such a process is disclosed in U.S. Pat. No. 4,061,819. In this manufacturing technique, relatively thin wood strands desirably are sorted according to length because, inter alia, the longer strand lengths enhance the properties of the final product. Since a large number of wood strands are required to manufacture the wood products, there is a need for a process and apparatus to rapidly sort the wood strands by length. The present method and apparatus was developed to fill this need.